Fan

ABSTRACT

A portable fan includes a casing having an air inlet, and an air outlet having an interior passage for receiving an air flow, and a mouth for emitting the air flow, the interior passage extending about an opening through which air is drawn by the air flow emitted from the mouth. The fan includes an impeller and a motor for rotating the impeller to generate an air flow between the air inlet and an air outlet which has a static pressure of at least 150 Pa downstream from the impeller. A filter unit is detachably connected to the casing. A filter of the filter unit is located upstream of the air inlet to remove airborne particulates from the air flow before it enters the casing.

REFERENCE TO RELATED APPLICATIONS

This application claims the priority of United Kingdom Application No.1004813.0 filed Mar. 23, 2010, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a portable fan. Particularly, but notexclusively, the present invention relates to a floor or table-top fan,such as a desk, tower or pedestal fan.

BACKGROUND OF THE INVENTION

A conventional domestic fan typically includes a set of blades or vanesmounted for rotation about an axis, and drive apparatus for rotating theset of blades to generate an air flow. The movement and circulation ofthe air flow creates a ‘wind chill’ or breeze and, as a result, the userexperiences a cooling effect as heat is dissipated through convectionand evaporation. The blades are generally located within a cage whichallows an air flow to pass through the housing while preventing usersfrom coming into contact with the rotating blades during use of the fan.

The use of fans in hospitals to keep patients cool is widespread, bothin general wards and in isolation wards. For example, depending on themedical condition of the patient it may be preferable to reduce the bodytemperature of the patient using a fan rather than by usingpharmaceuticals. When a fan is assigned to a patient, generally that fanis treated as an item of medical equipment and so, like other medicalequipment, will require frequent cleaning by a nurse or other hospitalemployee. The cleaning of bladed fans can be time consuming for theemployee, as the cage housing the blades of the fan needs to bedisassembled before the blades of the fan can be cleaned. Thisdisassembly usually requires the use of a screw driver, which cannot becarried by a nurse on a hospital ward. Often, it can be more convenientfor the hospital to engage a specialist cleaning company to clean thefan off site, although this can be very expensive.

WO 2009/030879 describes a fan assembly which does not use caged bladesto project air from the fan assembly. Instead, the fan assemblycomprises a base which houses a motor-driven impeller for drawing aprimary air flow into the base, and an annular nozzle connected to thebase and comprising an annular slot through which the primary air flowis emitted from the fan. The nozzle defines a central opening throughwhich air in the local environment of the fan assembly is drawn by theprimary air flow emitted from the mouth, amplifying the primary airflow.

The time required to clean off the external surfaces of this type of“bladeless” fan is much shorter than that required to clean a fan havingcaged blades, as there is no requirement to dismantle any parts of thefan to access any exposed parts of the fan. For example, the externalsurfaces of the fan may be wiped clean using a cloth. While this levelof cleaning may be sufficient for bladeless fans which are assigned topatients on general wards, when the bladeless fan is assigned to apatient in an isolation ward or infection containment ward there remainsa need to keep the internal components of the base clean to avoidcross-contamination when the fan is assigned to another patient.

SUMMARY OF THE INVENTION

The present invention provides a portable fan comprising a casing havingan air inlet; an air outlet comprising an interior passage for receivingan air flow, and a mouth for emitting the air flow, the interior passageextending about an opening through which air is drawn by the air flowemitted from the mouth; an impeller and a motor for rotating theimpeller to generate an air flow between the air inlet and an air outletwhich has a static pressure of at least 150 Pa downstream from theimpeller; and a filter unit detachably connected to the casing, thefilter unit comprising a filter located upstream of the air inlet.

The filter unit is preferably in the form of a disposable filter unitwhich can be replaced when, for example, the fan is assigned to adifferent patient, when the fan is moved with the patient from anisolation ward to a general ward, or when the filter has reached the endof a prescribed usage period. This can significantly reduce the costsassociated with the use of the fan, as the frequency with which the fanmay need to be taken off site for cleaning can be significantly reduced.The fan is arranged to generate an air flow with a static pressure of atleast 150 Pa, preferably in the range from 250 to 1.5 kPa, so that theair flow is not choked when the filter unit is attached to the casing.

The filter unit may be locatable over or around the casing so that thefilter is located upstream from the air inlet of the casing to removeairborne particulates from the air flow generated by the impeller beforethe air flow enters the casing. The filter unit is preferably manuallyconnectable to the casing to allow a user to attach the filter unit tothe fan, and subsequently detach the filter unit from the fan, withoutthe need for a tool.

The filter preferably comprises a high energy particle arrester (HEPA)filter. The filter may also comprise one or more of a foam, carbon,paper, or fabric filter. The filter preferably has a surface area in therange from 0.5 to 1.5 m² which is exposed to the air flow generated bythe fan. To minimize the volume of the filter, the filter is preferablypleated to form a filter which is substantially annular in shape forsurrounding the air inlet of the casing. In this case, the filter unitmay comprise two annular discs between which the filter is located.These discs can be easily wiped clean during use of the filter unit.Each disc may comprise a raised rim extending towards the other disc forretaining the filter between the discs. The filter may be readilyadhered to the discs during the construction of the filter unit. Thediscs may together be considered to form at least part of a filter unitto which the filter is adhered during construction of the filter unit.

The filter unit preferably comprises at least one seal for engaging anouter surface of the fan. This can enable the filter unit to form one ormore air-tight seals with the fan to ensure that the air flow generatedby the fan passes through the filter and not around the filter.Preferably, the filter unit is attachable to the casing so that thefilter is located over the air inlet of the fan. In a preferredembodiment the filter unit is in the form of a sleeve which is locatableabout an outer surface of a casing. Forming the filter unit in the formof a sleeve can enable the filter unit to be easily pushed or pulledover the casing of the fan as required. The filter unit may comprise afirst seal for engaging the casing of the fan, and a second seal forengaging the air outlet of the fan so that an air flow is drawn throughthe filter unit between the seals and through the filter. The casing maybe in the form of a base, which may be free-standing on a floor, desk,table or other surface.

The filter unit may comprise an outer cover comprising a plurality ofapertures through which air enters the filter unit. This outer cover canprovide a first, relatively coarse filter of the filter unit to preventairborne objects such as insects or large particles of dust from cominginto contact with the filter, and can prevent the filter from beingcontacted by a user, particularly during the attachment of the filterunit to the fan, and so prevent damage to the filter. The outer cover ispreferably transparent to allow a user to see the amount of dust ordebris which has been captured by the filter.

The casing may comprise a base surface and a side wall, with the airinlet being located in the side wall of the casing. The air inlet mayextend at least partially about the casing, and may comprise an array ofapertures. The casing may be substantially cylindrical in shape. Themotor and the impeller are preferably located within the casing. Adiffuser is preferably located downstream from the impeller.

The air outlet may be detachably connected to the filter unit. Part ofthe filter unit may be surrounded by part of the air outlet when thefilter unit is attached to the fan. For example, the air outlet maycomprise a base which is located over part of the filter unit when theair outlet is connected to the filter unit.

The casing may have a first connector, and the air outlet may have asecond connector. The filter unit may include a third connector, whichis substantially the same as the second connector, for co-operating withthe first connector to removably connect the filter unit to the casing,and a fourth connector, which is substantially the same as the firstconnector, for co-operating with the second connector to removablyconnect the air outlet to the filter unit. This can allow the air outletto be connected either directly to the casing, or for the filter unit tobe connected between the casing and the air outlet. The type ofconnection made between the filter unit and the casing, and between theair outlet and the filter unit, is the same as the type of connectionwhich is made between the air outlet and the casing in the absence ofthe filter unit. This facilitates the connection of the filter unit tothe casing and the air outlet, as the technique for connecting the airoutlet to the casing is the same as that for connecting the filter unitto the base, and for connecting the air outlet to the filter unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred features of the invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a front view of a fan;

FIG. 2 is a perspective view of the base of the fan of FIG. 1;

FIG. 3 is a perspective view of the air outlet of the fan of FIG. 1;

FIG. 4 is a lower perspective view of a portion of the air outlet of thefan of FIG. 1;

FIG. 5 is a sectional view of the fan of FIG. 1;

FIG. 6 is an enlarged view of part of FIG. 5;

FIG. 7 is a side view of an accessory for attachment to the fan of FIG.1;

FIG. 8 is a perspective view, from above, of the accessory of FIG. 7;

FIG. 9 is a sectional view of the accessory of FIG. 7;

FIG. 10 is a perspective view of the fan of FIG. 1 with the accessory ofFIG. 7 attached thereto; and

FIG. 11 is a sectional view of the fan of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a front view of a fan 10. The fan 10 is preferably in the formof a bladeless fan 10 comprising a base 12 and an air outlet 14connected to the base 12. With reference also to FIG. 2, the base 12comprises a substantially cylindrical outer casing 16 having a pluralityof air inlets 18 in the form of apertures formed in the outer casing 16and through which a primary air flow is drawn into the base 12 from theexternal environment. The base 12 further comprises a plurality ofuser-operable buttons 20 and a user-operable dial 22 for controlling theoperation of the fan 10. In this example the base 12 has a height in therange from 200 to 300 mm, and the outer casing 16 has an externaldiameter in the range from 100 to 200 mm.

As shown in FIG. 3, the air outlet 14 has an annular shape and definesan opening 24. The air outlet 14 has a height in the range from 200 to400 mm. The air outlet 14 comprises a mouth 26 located towards the rearof the fan 10 for emitting air from the fan 10 and through the opening24. The mouth 26 extends at least partially about the opening 24, andpreferably surrounds the opening 24. The inner periphery of the airoutlet 14 comprises a Coanda surface 28 located adjacent the mouth 26and over which the mouth 26 directs the air emitted from the fan 10, adiffuser surface 30 located downstream of the Coanda surface 28 and aguide surface 32 located downstream of the diffuser surface 30. Thediffuser surface 30 is arranged to taper away from the central axis X ofthe opening 24 in such a way so as to assist the flow of air emittedfrom the fan 10. The angle subtended between the diffuser surface 30 andthe central axis X of the opening 24 is in the range from 5 to 25°, andin this example is around 15°. The guide surface 32 is arranged at anangle to the diffuser surface 30 to further assist the efficientdelivery of a cooling air flow from the fan 10. The guide surface 32 ispreferably arranged substantially parallel to the central axis X of theopening 24 to present a substantially flat and substantially smooth faceto the air flow emitted from the mouth 26. A visually appealing taperedsurface 34 is located downstream from the guide surface 32, terminatingat a tip surface 36 lying substantially perpendicular to the centralaxis X of the opening 24. The angle subtended between the taperedsurface 34 and the central axis X of the opening 24 is preferably around45°. The overall depth of the air outlet 14 in a direction extendingalong the central axis X of the opening 24 is in the range from 100 to150 mm, and in this example is around 110 mm.

FIG. 5 illustrates a sectional view through the fan 10. The base 12comprises a lower base member 38, an intermediary base member 40 mountedon the lower base member 38, and an upper base member 42 mounted on theintermediary base member 40. The lower base member 38 has asubstantially flat bottom surface 43. The intermediary base member 40houses a controller 44 for controlling the operation of the fan 10 inresponse to depression of the user operable buttons 20 shown in FIGS. 1and 2, and/or manipulation of the user operable dial 22. Theintermediary base member 40 may also house an oscillating mechanism 46for oscillating the intermediary base member 40 and the upper basemember 42 relative to the lower base member 38. The range of eachoscillation cycle of the upper base member 42 is preferably between 60°and 120°, and in this example is around 90°. In this example, theoscillating mechanism 46 is arranged to perform around 3 to 5oscillation cycles per minute. A mains power cable 48 extends through anaperture formed in the lower base member 38 for supplying electricalpower to the fan 10.

The upper base member 42 may be tilted relative to the intermediary basemember 40 to adjust the direction in which the primary air flow isemitted from the fan 10. For example, the upper surface of theintermediary base member 40 and the lower surface of the upper basemember 42 may be provided with interconnecting features which allow theupper base member 42 to move relative to the intermediary base member 40while preventing the upper base member 42 from being lifted from theintermediary base member 40. For example, the intermediary base member40 and the upper base member 42 may comprise interlocking L-shapedmembers.

The upper base member 42 has an open upper end, and comprises an arrayof apertures 50 which extend at least partially about the upper basemember 42. The apertures 50 provide the air inlet 18 of the base 12. Theupper base member 42 houses an impeller 52 for drawing the primary airflow through the apertures 50 and into the base 12. Preferably, theimpeller 52 is in the form of a mixed flow impeller. The impeller 52 isconnected to a rotary shaft 54 extending outwardly from a motor 56. Inthis example, the motor 56 is a DC brushless motor having a speed whichis variable by the controller 44 in response to user manipulation of thedial 22. The maximum speed of the motor 56 is preferably in the rangefrom 5,000 to 10,000 rpm. The motor 56 is housed within a motor bucketcomprising an upper portion 58 connected to a lower portion 60. Themotor bucket is retained within the upper base member 42 by a motorbucket retainer 62. The upper end of the upper base member 42 comprisesa cylindrical outer surface 64. The motor bucket retainer 62 isconnected to the open upper end of the upper base member 42, for exampleby a snap-fit connection. The motor 56 and its motor bucket are notrigidly connected to the motor bucket retainer 62, allowing somemovement of the motor 56 within the upper base member 42.

Returning to FIG. 2, the upper end of the upper base member 42 comprisestwo pairs of open grooves 66 formed by removing part of the outersurface 64 to leave a shaped ‘cutaway’ portion. The upper end of each ofthe grooves 66 is in open communication with the open upper end of theupper base member 42. The open groove 66 is arranged to extenddownwardly from the open upper end of the upper base member 42. A lowerpart of the groove 66 comprises a circumferentially extending track 68having upper and lower portions bounded by the outer surface 64 of theupper base member 42. Each pair of open grooves 66 is locatedsymmetrically about the upper end of the upper base member 42, the pairsbeing spaced circumferentially from each other. An annular sealingmember 69 extends about the outer surface of the upper base member 42,and is located beneath the tracks 68 of the grooves 66.

The cylindrical outer surface 64 of the upper end of the upper basemember 42 further comprises a pair of wedge members 70 having a taperedpart 72 and a side wall 74. The wedge members 70 are located on oppositesides of the upper base member 42, with each wedge member 70 beinglocated within a respective cutaway portion of the outer surface 64.

The motor bucket retainer 62 comprises curved vane portions 76, 78extending inwardly from the upper end of the motor bucket retainer 62.Each curved vane 76, 78 overlaps a part of the upper portion 58 of themotor bucket. Thus the motor bucket retainer 62 and the curved vanes 76,78 act to secure and hold the motor bucket in place during movement andhandling. In particular, the motor bucket retainer 62 prevents the motorbucket from becoming dislodged and falling towards the air outlet 14 ifthe fan 10 becomes inverted.

With reference again to FIG. 5, one of the upper portion 58 and thelower portion 60 of the motor bucket comprises a diffuser 80 in the formof a stationary disc having spiral fins 82, and which is locateddownstream from the impeller 52. One of the spiral fins 82 has asubstantially inverted U-shaped cross-section when sectioned along aline passing vertically through the upper base member 42. This spiralfin 82 is shaped to enable a power connection cable to pass through thespiral fin 82 to the motor 56.

The motor bucket is located within, and mounted on, an impeller housing84. The impeller housing 84 is, in turn, mounted on a plurality ofangularly spaced supports 86, in this example three supports, locatedwithin the upper base member 42 of the base 12. A generallyfrusto-conical shroud 88 is located within the impeller housing 84. Theshroud 88 is preferably connected to the outer edges of the impeller 52,and is shaped so that the outer surface of the shroud 88 is in closeproximity to, but does not contact, the inner surface of the impellerhousing 84. A substantially annular inlet member 90 is connected to thebottom of the impeller housing 84 for guiding the primary air flow intothe impeller housing 84. The top of the impeller housing 84 comprises asubstantially annular air outlet 92 for guiding air flow emitted fromthe impeller housing 84 towards the air outlet 14.

Preferably, the base 12 further comprises silencing members for reducingnoise emissions from the base 12. In this example, the upper base member42 of the base 12 comprises a disc-shaped foam member 94 located towardsthe base of the upper base member 42, and a substantially annular foammember 96 located within the impeller housing 84.

A flexible sealing member is mounted on the impeller housing 84. Theflexible sealing member inhibits the return of air to the air inletmember 90 along a path extending between the outer casing 16 and theimpeller housing 84 by separating the primary air flow drawn in from theexternal environment from the air flow emitted from the air outlet 92 ofthe impeller 52 and the diffuser 80. The sealing member preferablycomprises a lip seal 98. The sealing member is annular in shape andsurrounds the impeller housing 84, extending outwardly from the impellerhousing 84 towards the outer casing 16. In the illustrated embodimentthe diameter of the sealing member is greater than the radial distancefrom the impeller housing 84 to the outer casing 16. Thus the outerportion 100 of the sealing member is biased against the outer casing 16and caused to extend along the inner face of the outer casing 16,forming a seal. The lip seal 98 of the preferred embodiment tapers andnarrows to a tip 102 as it extends away from the impeller housing 84 andtowards the outer casing 16. The lip seal 98 is preferably formed fromrubber.

The sealing member further comprises a guide portion 104 for guiding apower connection cable 106 to the motor 56. The guide portion 104 of theillustrated embodiment is formed in the shape of a collar and may be agrommet. The electrical cable 106 is in the form of a ribbon cableattached to the motor at joint 108. The electrical cable 106 extendingfrom the motor 56 passes out of the lower portion 60 of the motor bucketthrough spiral fin 82. The passage of the electrical cable 106 followsthe shaping of the impeller housing 84 and the guide portion 104 isshaped to enable the electrical cable 106 to pass through the flexiblesealing member. The guide portion 104 of the sealing member enables theelectrical cable 106 to be clamped and held within the upper base member42. A cuff 110 accommodates the electrical cable 106 within the lowerportion of the upper base member 42.

FIG. 6 illustrates a sectional view through the air outlet 14. The airoutlet 14 comprises an annular outer casing section 120 connected to andextending about an annular inner casing section 122. Each of thesesections may be formed from a plurality of connected parts, but in thisembodiment each of the outer casing section 120 and the inner casingsection 122 is formed from a respective, single molded part. The innercasing section 122 defines the central opening 24 of the air outlet 14,and has an external peripheral surface 124 which is shaped to define theCoanda surface 28, diffuser surface 30, guide surface 32 and taperedsurface 34.

The outer casing section 120 and the inner casing section 122 togetherdefine an annular interior passage 126 of the air outlet 14. Thus, theinterior passage 126 extends about the opening 24. The interior passage126 is bounded by the internal peripheral surface 128 of the outercasing section 120 and the internal peripheral surface 130 of the innercasing section 122. As shown in FIG. 4, the outer casing section 120comprises a base 132 having an inner surface 134. Formed on the innersurface 134 of the base 132 are two pairs of lugs 136 and a pair oframps 138 for connection to the upper end of the upper base member 42.Each lug 136 and each ramp 138 upstands from the inner surface 134. Thusthe base 132 is connected to, and over, the open upper end of the motorbucket retainer 62 and the upper base member 42 of the base 12. Thepairs of lugs 136 are located around the outer casing section 120 andspaced from each other so that the pairs of lugs 136 correspond to thespaced arrangement of the pairs of open grooves 66 of the upper end ofthe upper base member 42 and so that the location of the pair of ramps138 corresponds to the location of the pair of wedge members 70 of theupper end of the upper base member 42.

The base 132 of the outer casing section 120 comprises an aperturethrough which the primary air flow enters the interior passage 126 ofthe air outlet 14 from the upper end of the upper base member 42 and theopen upper end of the motor bucket retainer 62.

The mouth 26 of the air outlet 14 is located towards the rear of the fan10. The mouth 26 is defined by overlapping, or facing, portions 140, 142of the internal peripheral surface 128 of the outer casing section 120and the external peripheral surface 124 of the inner casing section 122,respectively. In this example, the mouth 26 is substantially annularand, as illustrated in FIG. 4, has a substantially U-shapedcross-section when sectioned along a line passing diametrically throughthe air outlet 14. In this example, the overlapping portions 140, 142 ofthe internal peripheral surface 128 of the outer casing section 120 andthe external peripheral surface 124 of the inner casing section 122 areshaped so that the mouth 26 tapers towards an outlet 144 arranged todirect the primary flow over the Coanda surface 28. The outlet 144 is inthe form of an annular slot, preferably having a relatively constantwidth in the range from 0.5 to 5 mm. In this example the outlet 144 hasa width of around 1 mm. Spacers may be spaced about the mouth 26 forurging apart the overlapping portions 140, 142 of the internalperipheral surface 128 of the outer casing section 120 and the externalperipheral surface 124 of the inner casing section 122 to maintain thewidth of the outlet 144 at the desired level. These spacers may beintegral with either the internal peripheral surface 128 of the outercasing section 120 or the external peripheral surface 124 of the innercasing section 122.

Referring to FIGS. 3 and 4, to attach the air outlet 14 to the base 12,the air outlet 14 is inverted from the orientation illustrated in FIG. 4and the base 132 of the air outlet 14 is located over the open upper endof the upper base member 42. The air outlet 14 is aligned relative tothe base 12 so that the lugs 136 of the base 132 of the air outlet 14are located directly in line with the open upper ends of the opengrooves 66 of the upper base member 42. In this position the pair oframps 138 of the base 132 is directly in line with the pair of wedgemembers 70 of the upper base member 42. The air outlet 14 is then pushedon to the base 12 so that the lugs 136 are located at the base of theopen grooves 66. The sealing member 69 of the base 12 engages the innersurface 134 of the base 132 of the air outlet 14 to form an air-tightseal between the base 12 and the air outlet 14.

To secure the air outlet 14 to the base 12, the air outlet 14 is rotatedin a clockwise direction relative to the base 12 so that the lugs 136move along the circumferentially extending tracks 68 of the open grooves66. The rotation of the air outlet 14 relative to the base 12 alsoforces the ramps 138 to run up and slide over the tapers 72 of the wedgemember 70 through localized elastic deformation of the open upper end ofthe upper base member 42. With continued rotation of the air outlet 14relative to the base 12, the ramps 138 are forced over the side walls 74of the wedge members 70. The open upper end of the upper base member 42relaxes so that the ramps 138 are generally radially aligned with thewedge members 70. Consequently, the side walls 74 of the wedge members70 prevent accidental rotation of the air outlet 14 relative to the base12, whereas the location the lugs 136 within the tracks 68 preventslifting of the air outlet 14 away from the base 12. The rotation of theair outlet 14 relative to the base 12 does not require excessiverotational force and so the assembly of the fan 10 may be carried out bya user.

To operate the fan 10 the user depresses an appropriate one of thebuttons 20 on the base 12, in response to which the controller 44activates the motor 56 to rotate the impeller 52. The rotation of theimpeller 52 causes a primary air flow to be drawn into the base 12through the air inlet 18. Depending on the speed of the motor 56, theprimary air flow generated by the impeller 52 may be between 20 and 30litres per second. The pressure of the primary air flow at the outlet 92of the base 12 may be at least 150 Pa, and is preferably in the rangefrom 250 to 1.5 kPa. The primary air flow passes sequentially throughthe impeller housing 84, the upper end of the upper base member 42 andopen upper end of the motor bucket retainer 62 to enter the interiorpassage 126 of the air outlet 14. The primary air flow emitted from theair outlet 92 of the base 12 is generally in an upward and forwarddirection.

Within the air outlet 14, the primary air flow is divided into two airstreams which pass in opposite directions around the central opening 24of the air outlet 14. Part of the primary air flow entering the airoutlet 14 in a sideways direction (generally orthogonal to the axis X)passes into the interior passage 126 in a sideways direction withoutsignificant guidance, whereas another part of the primary air flowentering the air outlet 14 in a direction parallel to the axis X isguided by the curved vanes 76, 78 of the motor bucket retainer 62 toenable the air flow to pass into the interior passage 126 in a sidewaysdirection. As the air streams pass through the interior passage 126, airenters the mouth 26 of the air outlet 14. The air flow into the mouth 26is preferably substantially even about the opening 24 of the air outlet14. Within each section of the mouth 26, the flow direction of theportion of the air stream is substantially reversed. The portion of theair stream is constricted by the tapering section of the mouth 26 andemitted through the outlet 98.

The primary air flow emitted from the mouth 26 is directed over theCoanda surface 28 of the air outlet 14, causing a secondary air flow tobe generated by the entrainment of air from the external environment,specifically from the region around the outlet 98 of the mouth 26 andfrom around the rear of the air outlet 14. This secondary air flowpasses through the central opening 24 of the air outlet 14, where itcombines with the primary air flow to produce a total air flow, or aircurrent, projected forward from the air outlet 14. Depending on thespeed of the motor 56, the mass flow rate of the air current projectedforward from the fan 10 may be in the range from 300 to 400 litres persecond, and the maximum speed of the air current may be in the rangefrom 2.5 to 4 m/s.

The even distribution of the primary air flow along the mouth 26 of theair outlet 14 ensures that the air flow passes evenly over the diffusersurface 30. The diffuser surface 30 causes the mean speed of the airflow to be reduced by moving the air flow through a region of controlledexpansion. The relatively shallow angle of the diffuser surface 30 tothe axis X of the opening 24 allows the expansion of the air flow tooccur gradually. A harsh or rapid divergence would otherwise cause theair flow to become disrupted, generating vortices in the expansionregion. Such vortices can lead to an increase in turbulence andassociated noise in the air flow which can be undesirable, particularlyin a domestic product such as a fan. The air flow projected forwardsbeyond the diffuser surface 30 can tend to continue to diverge. Theguide surface 32 extending inwardly towards the axis X converges the airflow towards the axis X. As a result, the air flow can travelefficiently out from the air outlet 14, enabling rapid air flow to beexperienced at a distance of several meters from the fan 10.

FIGS. 7 to 9 illustrate an external accessory for the fan 10. Theaccessory is in the form of a filter unit 200 which is detachablyattachable to the fan 10 to allow the filter unit 200 to be removed forcleaning or replacement.

The filter unit 200 is in the form of a generally cylindrical sleevewhich is locatable around the upper base member 42 of the base 12 sothat the filter unit 200 is located over the air inlet 18 of the fan 10,as illustrated in FIGS. 10 and 11. This allows the filter unit 200 toremove airborne particles from the primary air flow generated by the fan10 before the primary air flow enters the base 12 of the fan 10.

The filter unit 200 comprises a generally annular filter 202 forremoving airborne particles from the primary air flow. The filter 202 ispreferably in the form of a radially pleated high energy particlearrester (HEPA) filter. The filter 202 has a surface area that isexposed to the incoming primary air flow generated by the fan which isin the range from 0.5 to 1.5 m², and in this example is around 1.1 m².The filter 202 is surrounded by a cylindrical outer cover 204, which ispreferably formed from plastics material, to protect the filter 202 andthus allows a user to handle the filter unit 200 without contacting thefilter 202. The cover 204 is preferably transparent to allow a user toexamine visually the state of the filter 202 during use or after aperiod of use. The cover 204 comprises a plurality of apertures (notshown) through which the primary air flow enters the filter unit 200,and thus provides a relatively coarse first stage of filtration of thefilter unit 200 to prevent relatively large airborne objects or insectsfrom entering the filter unit 200. The filter unit 200 may furthercomprise additional filter media between the filter 202 and the cover204, or downstream from the filter 202. For example, this additionalfilter media may comprise one or more of foam, carbon, paper, or fabric.

The filter 202 and the cover 204 are sandwiched between two annularplates 206, 208 of the filter unit 200. Each plate 206, 208 includes acircular inner rim 210 and a circular outer rim 212 which both extendpartially towards the other plate 206, 208. The filter 202 and the cover204 are located between the rims 210, 212 of the plates 206, 208, andare preferably secured to the plates 206, 208 using an adhesive.

The upper plate 206 comprises a lower collar 214 which is locatedradially inwardly from the inner rim 210 of the upper plate 206. Thelower collar 214 extends axially downwards from the upper plate 206. Theinner diameter of the lower collar 214 is substantially the same as theinner diameter of the base 132 of the air outlet 14 of the fan 10.Similar to the base 132 of the air outlet 14, the inner surface of thelower collar 214 comprises two pairs of lugs 216 and a pair of ramps(not shown) for connection to the upper end of the upper base member 42of the base 12 of the fan 10. The shape of the lugs 216 and the ramps ofthe lower collar 214, and the angular spacing between the lugs 216 andthe ramps of the lower collar 214, are substantially identical to thoseof the lugs 136 and ramps 138 of the base 132 of the air outlet 14.

The upper plate 206 further comprises an upper collar 218 which islocated radially inwardly from the lower collar 214. The upper collar218 extends axially upwards from the inner circumferential periphery ofthe upper plate 208. The outer diameter of the upper collar 218 issubstantially the same as the outer diameter of the outer surface 64 ofthe open upper end of the upper base member 42. Similar to the upperbase member 42, the upper collar 218 comprises two pairs of open grooves220 and a pair of wedge members 222. The open grooves 220 aresubstantially identical to the open grooves 66 of the outer surface 64of the upper base member 42, and the spacing between the open grooves220 is substantially the same as that between the open grooves 66. Thewedge members 222 are substantially identical to the wedge members 70 ofthe outer surface 64 of the upper base member 42, and the spacingbetween the wedge members 222 is substantially the same as that betweenthe wedge members 70. A first annular sealing member 224 of the filterunit 200 extends about the outer surface of the upper collar 218, and islocated beneath the circumferentially extending tracks 226 of thegrooves 220.

The collars 214, 218 are preferably integral with the upper plate 206,which is preferably formed from plastics material.

The lower plate 208 includes a relatively small collar 228 which extendsaxially downwardly from the inner rim 210 of the lower plate 208. Thecollar 228 comprises a circumferentially extending groove located on itsinner surface. A second annular sealing member 230 of the filter unit200 is located within this groove. The collar 228 is preferably integralwith the lower plate 208, which is also preferably formed from aplastics material.

To attach the filter unit 200 to the fan 10, first the air outlet 14 isdetached from the base 12. To detach the air outlet 14 from the base 12,the air outlet 14 is twisted relative to the base 12 in the oppositedirection (anti-clockwise) to that for attaching the air outlet 14 tothe base 12. With a suitable torque applied manually by the user, theupper end of the upper base member 42 is again caused to flex locallyradially inwardly. This localized deformation of the upper base member42 allows the ramp 138 to be rotated over the wedge members 70, whilethe lugs 136 are moved simultaneously along the tracks 68 of the grooves66. Once the lugs 136 reach the ends of the tracks 68, the air outlet 14may be lifted from the base 12.

Although the detachment of the air outlet 14 from the base 12 requires agreater force to be applied to the air outlet 14 than the force requiredfor attachment, the resilience of the upper base member 42 is selectedso that the detachment of the air outlet 14 may be performed manually

The user then attaches the filter unit 200 to the base 12. The techniquefor attaching the filter unit 200 to the base 12 is essentially the sameas that for attaching the air outlet 14 to the base 12. The user locatesthe open lower end of the collar 228 of the lower plate 208 over theopen upper end of the upper base member 42, and lowers the filter unit200 around the base 12. When the bottom end of the lower collar 214 ofthe upper plate 206 is located immediately above the open upper end ofthe upper base member 42, the user rotates the filter unit 200 until thelugs 216 of the filter unit 200 are located directly in line with theopen upper end of the open grooves 66 of the upper base member 42. Inthis position the pair of ramps of the filter unit is directly in linewith the pair of wedge members 70 of the upper base member 42. Thefilter unit 200 is then pushed further on to the base 12 so that thelugs 216 of the filter unit 200 are located at the base of the opengrooves 66 of the base 12. To secure the filter unit 200 to the base 12,the filter unit 200 is rotated in a clockwise direction relative to thebase 12 so that the lugs 216 move along the circumferentially extendingtracks 68 of the open grooves 66. The rotation of the filter unit 200relative to the base 12 also forces the ramps to run up and slide overthe tapers 72 of the wedge members 70 through localized elasticdeformation of the upper base member 42. With continued rotation of thefilter unit 200 relative to the base 12, the ramps are forced over theside walls 74 of the wedge members 70. The upper base member 42 relaxesso that the ramps are generally radially aligned with the wedge members70. Consequently, the side walls 74 of the wedge members 70 preventaccidental rotation of the filter unit 200 relative to the base 12,whereas the location the lugs 216 within the tracks 68 prevents liftingof the filter unit 200 away from the base 12.

As shown in FIG. 11, when the filter unit 200 is attached to the base 12the second sealing member 230 of the filter unit 200 is located beneaththe air inlet 18 of the base 12, and engages the outer surface of thebase 12 to form an air-tight seal between the base 12 and the filterunit 200. As also shown in FIG. 10, the buttons 22 and user operabledial 22 of the base 12 remain accessible by the user when the filterunit 200 is attached to the base 12.

The air outlet 14 is then attached to the filter unit 200. Theattachment of the air outlet 14 to the filter unit 200 is essentiallythe same as the attachment of the air outlet 14 to the base 12. The base132 of the air outlet 14 is located over the upper collar 218 of thefilter unit 200, and the air outlet 14 is aligned relative to the base12 so that the lugs 136 of the base 132 of the air outlet 14 are locateddirectly in line with the open upper end of the open grooves 220 of thefilter unit 200. The air outlet 14 is then pushed on to the filter unit200 so that the lugs 136 are located at the base of the open grooves220. The first sealing member 224 of the filter unit 200 engages theinner surface 134 of the base 132 of the air outlet 14 to form anair-tight seal between the filter unit 200 and the air outlet 14. Again,to secure the air outlet 14 to the filter unit 200 the air outlet 14 isrotated in a clockwise direction relative to the filter unit 200 so thatthe lugs 136 move along the circumferentially extending tracks 226 ofthe open grooves 220 of the filter unit 200. The rotation of the airoutlet 14 relative to the filter unit 200 also forces the ramps 138 torun up and slide over the tapers of the wedge members 222 of the filterunit 200 through localized elastic deformation of the upper collar 218.With continued rotation of the air outlet 14 relative to the filter unit200, the ramps 138 are forced over the side walls of the wedge members220. The upper collar 218 relaxes so that the ramps 138 are generallyradially aligned with the wedge members 220. Consequently, the sidewalls of the wedge members 200 prevent accidental rotation of the airoutlet 14 relative to the filter unit 200, whereas the location the lugs136 within the tracks 226 of the grooves 200 prevents lifting of the airoutlet 14 away from the filter unit 200.

The assembled combination of the fan 10 and the filter unit 200 is shownin FIGS. 10 and 11. The air-tight seals that the filter unit 200 makeswith the base 12 and the air outlet 14 force the primary air flow topass through the filter 202 of the filter unit 200 to remove airborneparticulates from the primary air flow before it enters the base 12. Inaddition to purifying the air in the local environment of the fan 10,the removal of airborne particulates from the primary air flow before itenters the base 12 can significantly reduce the rate at which dust anddebris can build-up on the internal components of the fan 10, therebyreducing the frequency at which the fan 10 needs to be cleaned. Thefilter unit 200 may be easily replaced for cleaning or replacement bydetaching the air outlet 14 from the filter unit 200, which is performedin the same manner as the removal of the air outlet 14 from the base 12,and subsequently detaching the filter unit 200 from the base 12. Thiscan be performed quickly and easily without the use of any tools. Whenthe use of the filter unit 200 is no longer required, the filter unit200 can be rapidly removed from the fan 10 by detaching the filter unit200 from the base 12, and re-attaching the air outlet 14 directly to thebase 12.

1. A portable fan comprising: a casing having an air inlet; an airoutlet comprising an interior passage for receiving an air flow, and amouth for emitting the air flow, the interior passage extending about anopening through which air is drawn by the air flow emitted from themouth; an impeller and a motor for rotating the impeller to generate anair flow between the air inlet and an air outlet which has a staticpressure of at least 150 Pa downstream from the impeller; and a filterunit detachably connected to the casing, the filter unit comprising afilter located upstream of the air inlet.
 2. The fan of claim 1, whereinthe motor and the impeller are arranged to generate an air flow having astatic pressure in the range from 250 to 1.5 kPa.
 3. The fan of claim 1,wherein the filter unit comprises at least one seal for engaging anouter surface of the casing.
 4. The fan of claim 1, wherein the filterunit is in the form of a sleeve locatable about the casing.
 5. The fanof claim 1, wherein the filter is substantially annular in shape.
 6. Thefan of claim 5, wherein the filter unit comprises two annular discsbetween which the filter is located.
 7. The fan of claim 6, wherein eachdisc comprises a raised rim extending towards the other disc forretaining the filter between the discs.
 8. The fan of claim 6, whereinthe filter is adhered to the discs.
 9. The fan of claim 1, wherein thefilter unit comprises a filter housing, and the filter is adhered to thefilter housing.
 10. The fan of claim 1, wherein the filter unitcomprises an outer cover comprising a plurality of apertures.
 11. Thefan of claim 1, wherein the casing comprises a base surface and a sidewall, and wherein the air inlet is located in the side wall of thecasing.
 12. The fan of claim 1, wherein the air inlet extends at leastpartially about the casing.
 13. The fan of claim 1, wherein the airinlet comprises an array of apertures.
 14. The fan of claim 1, whereinthe casing is substantially cylindrical in shape.
 15. The fan of claim1, wherein the air outlet is detachably connected to the filter unit.16. The fan of claim 1, wherein the filter unit comprises a first sealfor engaging the casing, and a second seal for engaging the air outlet.